Conformal coatings are protective coatings that conform to the surface of electronic components and circuit board assemblies. Properly applied conformal coatings can increase the working life of the assemblies by protecting its components and the board itself. Proper coverage and uniformity of the conformal coating over the assembly is critical for effective protection of the assembly. It can be difficult, however, to determine the integrity and uniformity of the conformal coating when it is coated on an assembly. Therefore, the conformal coating material is sometimes doped with a fluorescent dye or “tracer” to aid in the quality assurance inspection of the assembly for proper coverage.
Fluorescent dyes such as, for example, thioxanthene compounds, work well for imparting color to certain plastic materials such as, for example, polymethacrylate, polycarbonate, polystyrene, and polyester. Most fluorescent dyes, however, have poor or limited solubility in certain polymer matrixes. For instance, most fluorescent dyes have poor or no compatibility with fluorochemical monomers and polymers. This results in poor color quality and dye bleed and little or no color entrainment into the resulting fluoropolymer. Fluoropolymers containing dyes are therefore typically not used when leaching and toxicity issues are of concern (for example, in food packaging and medical applications). There is also little advantage in adding most dyes to fluoropolymer conformal coatings since the dyes typically do not entrain uniformly throughout the coating such that they are useful during quality control inspection.